1. Field of the Invention
This invention relates to a surface fastener molded of thermoplastic resin and having a multiplicity of engaging elements on the front surface of a substrate sheet and a backing sheet integrally joined with the rear surface of the substrate sheet, and also to a method of continuously manufacturing such molded surface fastener. More particularly, the invention relates to a molded surface fastener which secures adequate flexibility and effectively prevents any crack in a substrate sheet and which is firmly supported by a backing sheet to enable a wide variety of applications, and also to a method of effectively manufacturing such molded surface fastener.
2. Description of the Related Art
A molded surface fastener of the described type is known in which a multiplicity of engaging elements is molded on the front surface of a substrate sheet and a backing sheet is integrally joined with the rear surface of the substrate sheet by pressing the backing sheet against the substrate sheet in a semi-molten state. This known art is exemplified by Japanese Utility Model Publication No. Sho 55-55602. In this publication, fiber material such as a knit or a woven fiber fabric, a non-woven cloth, a paper sheet are fused on the rear surface of a molded surface fastener in which a multiplicity of hook elements are integrally molded on the front surface of a substrate sheet. This publication merely shows the idea of pressing the fiber material against the substrate sheet while it is in semi-molten state but is totally silent about a concrete method for manufacturing such molded surface fastener.
Methods for manufacturing such molded surface fastener are disclosed in, for example, U.S. Pat. Nos. 5,260,015 and 5,441,687. According to these U.S. Patents, while molten resin is introduced to the circumferential surface of a rotating die wheel, which has a multiplicity of engaging-element-forming cavities on the circumferential surface, to continuously mold on the wheel surface a substrate sheet and a multiplicity of engaging elements standing on the front surface of the substrate sheet, a backing sheet is integrally joined with the rear surface of the substrate sheet by pressing the backing sheet against the substrate sheet in semi-molten state by a pressing roller or other pressing means.
However, in the molded surface fastener disclosed in the above-mentioned publications, since the circumferential surface of the pressing roller, which presses the backing sheet against the substrate sheet, is flat entirely, the backing sheet is joined integrally with the entire rear surface of the substrate sheet. As is understood from a common knowledge that the joint surface, which is produced between the substrate sheet and the backing sheet would be rigid, the molded surface fastener with backing described above is very rigid throughout its entire surface and is therefore not suitable for modern molded surface fasteners to which an increased degree of flexibility is required.
Applications of this type molded surface fasteners, with or without backing, in various industrial fields are on the increase in recent years. For example, they are popular as fasteners for various kinds of bags, clothing, and other daily goods as well as for disposable diapers, interior ornaments, and various kinds of industrial materials such as sheet materials and machine parts. Molded surface fasteners to be used in various industrial fields should vary in characteristics to meet with a wide variety of demands. For use in disposable diapers, the molded fasteners should be excellent in softness and small in size but require a limited durability enough for repeated attaching operations two or three times. On the other hand, for use in fastening industrial materials, they require adequate rigidity and excellent engaging toughness and should have such a structure that the materials can be fastened surely by only a single fastening operation.
Flexible manufacturing is therefore inevitable to manufacture such molded surface fasteners different in size and shape to meet with various kinds of demands for functions.
For use in fastening interior ornaments in a car, mere variation of size and shape does not meet with the demands; for example, the molded surface fastener itself should be formed complementarily with a curved wall surface of a car in order to fasten an interior ornament on the wall. Further, on occasions, it is needed to tentatively attach the molded surface fastener to a tentative-attachment member. If the tentative-attachment member is made of magnetic metal such as iron, it is necessary to magnetize the molded surface fastener.
For providing the molded surface fastener with such function, merely changing the size and/or shape does not suffice. None of the conventional molded surface fasteners including those disclosed in the above-mentioned publications do satisfy all the foregoing demands.